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2017 Atlantic hurricane season (Reimagined by the GFS)
The Global Forecast System (GFS) is the primary short-to-medium range global synoptic model operated by the National Centers for Environmental Prediction (NCEP). The GFS runs four times daily and forecasts out to 384 hours (16 days). Within this range, the GFS is liable to forecast the formation and development of subtropical and tropical cyclones. While the GFS does show relatively remarkable accuracy for the most part, it too can fall victim to phantom storms and overly bullish forecasting – between 2004 and 2011, the GFS forecast 133 correct cyclogenesis scenarios but produced 250 false alarms. If we took the worst-case scenario runs from the GFS, what would the 2017 Atlantic hurricane season look like? This page seeks to find out that answer. Certain rules apply for model storms to be included, however – see rules. Rules The GFS and its sister models typically produce numerous modelcanes over the course of a season (perhaps 50 or more unique events). Many of these cyclogenesis events, however, are transient, and only appear for one or two runs. To maintain consistency and filter out these errant solutions, the following rules apply for storm inclusion on this page: *Tracks and storms are based on the worst-case scenario from the operational GFS, with some liberties taken on the track depictions if the storm remained active at the end of the selected GFS run. That also means no GFS-Parallel or GFS-Ensemble storms or storms from other models. **If the strongest run for an actual storm came before the storm formed, then the modelcane is selected over runs while the storm was active. *The operational GFS must have depicted the development of the subtropical/tropical cyclone for at least four runs before truncation (240 hours) or eight runs total (before or after truncation, and out to 384 hours); the strongest of these runs is depicted here. What is considered a cyclogenesis event and the classification of model solutions as unique or repeated cyclogenesis events is at the discretion of the author of this page. *If the actual storm was stronger than any GFS run (including runs while the storm was still active), or more of a worst case scenario, the strongest GFS run is chosen regardless. This, of course, is rare. *More attention was given to the GFS after June 1; thus, activity depicted here prior to June 1 may not be true to the GFS' actual modelling trends. *Storm strength is at the discretion of the editor of this page, but is generally based on GFS run data. Occasionally storm winds are based on Brown et. al (2005). *Storm names are listed as if the storms did indeed form at the times depicted. Thus a storm's name may differ from what it actually was in reality (e.g. GFS Cindy in the Gulf of Mexico formed prior to GFS Bret in the Central Atlantic, and thus they are shown here as Bret and Cindy, respectively). What are the intensities for the storms based on? *Points on the track are based on the GFS high-resolution surface pressures. *What is considered a tropical depression or not is at the discretion of the author of this page. *A tropical storm must have 10m gale-force winds explicitly depicted on the GFS. *Storms classified on the Saffir-Simpson hurricane wind scale (a.k.a. hurricanes) are based on pressure-wind relationships devised in Brown (2005) and Landsea, et. al (2004). *Classification of the storms on this page are based on pressure-wind relationships described in the previous papers, and are not based on the explicit peak winds on the GFS output. The author of this page may utilize the relationship described in Knaff-Zehr-Courtney (2009) to derive more specific results for stronger storms. *Pressures for the storms listed are generally based on the GFS high-resolution surface pressures. Past 240 hours, however, the author of this page uses a basic linear formula to reduce GFS pressures to account for the reduced GFS resolution past 240 hours. Season summary Timeline ImageSize = width:750 height:220 PlotArea = top:10 bottom:80 right:20 left:20 Legend = columns:3 left:30 top:58 columnwidth:270 AlignBars = early DateFormat = dd/mm/yyyy Period = from:01/04/2017 till:01/12/2017 TimeAxis = orientation:horizontal ScaleMinor = grid:black unit:month increment:1 start:01/04/2017 Colors = id:canvas value:gray(0.88) id:GP value:red id:TD value:rgb(0.38,0.73,1) legend:Tropical_Depression_=_<39_mph_(0-62_km/h) id:TS value:rgb(0,0.98,0.96) legend:Tropical_Storm_=_39-73_mph_(63-117 km/h) id:C1 value:rgb(1,1,0.80) legend:Category_1_=_74-95_mph_(119-153_km/h) id:C2 value:rgb(1,0.91,0.46) legend:Category_2_=_96-110_mph_(154-177_km/h) id:C3 value:rgb(1,0.76,0.25) legend:Category_3_=_111-130_mph_(178-209-km/h) id:C4 value:rgb(1,0.56,0.13) legend:Category_4_=_131-155_mph_(210-249_km/h) id:C5 value:rgb(1,0.38,0.38). legend:Category_5_=_>=156_mph_(>=250_km/h) Backgroundcolors = canvas:canvas BarData = barset:Hurricane bar:Month PlotData= barset:Hurricane width:10 align:left fontsize:S shift:(4,-4) anchor:till from:19/04/2017 till:21/04/2017 color:TS text:"Arlene (TS)" from:28/05/2017 till:07/06/2017 color:C4 text:"Bret (C4)" from:09/06/2017 till:11/06/2017 color:TD text:"Three (TD)" from:18/06/2017 till:27/06/2017 color:C1 text:"Cindy (C1)" from:20/06/2017 till:26/06/2017 color:C1 text:"Don (C1)" from:25/06/2017 till:03/07/2017 color:TS text:"Emily (TS)" from:04/07/2017 till:19/07/2017 color:C5 text:"Franklin (C5)" from:11/07/2017 till:25/07/2017 color:C5 text:"Gert (C5)" from:18/07/2017 till:20/07/2017 color:TS text:"Harvey (TS)" barset:break from:30/07/2017 till:11/08/2017 color:C3 text:"Irma (C3)" from:04/08/2017 till:17/08/2017 color:C4 text:"Jose (C4)" from:07/08/2017 till:10/08/2017 color:C3 text:"Katia (C3)" from:14/08/2017 till:18/08/2017 color:C3 text:"Lee (C3)" from:14/08/2017 till:25/08/2017 color:C4 text:"Maria (C4)" from:16/08/2017 till:20/08/2017 color:C4 from:21/08/2017 till:30/08/2017 color:C4 text:"Ophelia (C4)" from:26/08/2017 till:06/09/2017 color:TS text:"Philippe (TS)" barset:break barset:skip barset:skip barset:skip barset:skip barset:skip from:23/08/2017 till:29/08/2017 color:C4 text:"Nate (C4)" bar:Month width:5 align:center fontsize:S shift:(0, -20) anchor:middle color:canvas from:01/04/2017 till:01/05/2017 text:April from:01/05/2017 till:30/05/2017 text:May from:01/06/2017 till:01/07/2017 text:June from:01/07/2017 till:01/08/2017 text:July from:01/08/2017 till:01/09/2017 text:August from:01/09/2017 till:01/10/2017 text:September from:01/10/2017 till:01/11/2017 text:October from:01/11/2017 till:30/11/2017 text:November Model depictions File:GFS_June_2017.jpg|The GFS in June 2017 (all runs, non-filtered) File:GFS_July_2017.png|The GFS in July 2017 (all runs, non-filtered) Storms Tropical Storm Arlene Hurricane Bret :In reality: Nothing happened; Run chosen: May 21, 06Z In late May, an area of disturbed weather persisted in the western Caribbean Sea, associated with the development of a broad monsoonal gyre over Central America. Beginning May 26, a low-pressure area began to coalesce just north of Honduras. At 12:00 UTC on May 28, the disturbance became sufficiently organized to be considered a tropical cyclone—since gale-force winds were already present, the system was classified as Tropical Storm Bret. Upon cyclogenesis, steering currents were weak, causing Bret to drift slowly in the western Caribbean; warm waters allowed for gradual strengthening. Beginning on May 30, a weak northerly flow induced by a passing trough caused Bret to move northward. On May 31, Bret intensified into a hurricane and curved northwestward. An eye emerged on satellite imagery as Bret made landfall just north of Cancun as a Category 1 hurricane with maximum sustained winds of 80 mph (130 km/h) at 15:00 UTC on June 1. Despite moving over the Yucatan Peninsula, proximity to water allowed Bret to continue strengthening; radar indicated a strengthening eyewall as the hurricane tracked over land. Fifteen hours after landfall, Bret emerged into the Gulf of Mexico and reached Category 2 intensity. Another passing trough steered Bret northward over the next few days, bringing it over the central Gulf. With conditions continuing to be conducive for development, Bret commenced a period of unusually steady deepening beginning on June 3. Bret reached major hurricane strength on June 4, followed by Category 4 strength a day later. Concurrently, the strengthening storm began to curve eastward in response to the progression of the upper-trough, although a strengthening ridge to Bret's west hindered the cyclone's forward motion. At 06:00 UTC on June 6, Bret reached its peak intensity with winds of 145 mph (230 km/h) and a minimum barometric pressure of 929 mbar (hPa; 27.43 inHg), making it the strongest June tropical cyclone in the Atlantic on record. Although upwelling did not serve to hinder the hurricane significantly over the deeper waters of the Gulf of Mexico, the combination of shallower waters off western Florida and a slowly worsening upper-level air environment caused Bret to weaken somewhat as it approached the peninsula. At 00:00 UTC on June 7, Bret made landfall near South Venice with winds of 125 mph (200 km/h) and a pressure of 945 mbar (hPa; 27.91 inHg); this made Bret a Category 3 at landfall and the first major hurricane to strike the United States since Hurricane Wilma in 2005 and the strongest one to do so in June. The storm gradually weakened as it traversed the Florida peninsula, degenerating into a tropical storm as it emerged into the Atlantic later that day. Accelerating into open oceanic waters, Bret transitioned into an extratropical cyclone on June 8. These extratropical remnants passed just south of Bermuda before dissipating on June 9. Mandatory evacuations were issued for portions of Cancun as Bret approached on May 31, curtailing the emerging summer tourist operations in the region. The storm's strongest winds were weighted north of the circulation and away from populated areas at landfall; however, strong winds, peaking at 59 mph (95 km/h), caused widespread power outages affecting some 125,000 customers. The majority of Bret's effects in the Yucatan Peninsula was from heavy rainfall exacerbated by the storm's slow motion—some US$450 million in agricultural damages were attributed to destroyed crops caused by flooding rains. Overall, damage from Bret in Mexico totaled US$737 million, along with 2 deaths. Already an unusually powerful storm for its time, Bret was the first hurricane to threaten Florida's Cultural Coast since Hurricane Charley in 2004 Atlantic hurricane season. Nearly 150,000 people were evacuated from coastal areas of Charlotte and Sarasota counties in advance of the system, with numerous shelters activated throughout Florida. Bret's winds had unusual staying power over Florida as a result of baroclinic interactions, producing powerful gusts throughout its track across the peninsula. Hurricane-force winds were felt throughout Port Charlotte and well inland. The strong winds caused power outages affecting nearly a million people and destroyed numerous structures and toppled swaths of trees. Damage in the United States totaled US$9.1 billion, along with six fatalities. Tropical Depression Three :In reality: Nothing happened; Run chosen: June 7, 12Z In mid-June, an area of convection persisted in the Gulf of Panama. In an environment conducive for tropical cyclogenesis, a small area of low pressure developed within the convective envelope and tracked northward across the isthmus of Panama and into the southwestern Caribbean Sea on June 8. The system quickly developed, and on 18:00 UTC June 9 became sufficiently organized to be classified as Tropical Depression Three roughly 70 mi (115 km) northwest of Colón, Panama. Despite the earlier developmental trends, Three failed to organize much further after cyclogenesis. Tracking slowly westward under the influence of the low-level easterly tradewind flow, Three eventually made landfall near Bluefields, Nicaragua with winds of 30 mph (50 km/h) on June 11. Continuing inland, Three dissipated later that day over Nicaragua. Hurricane Cindy :In reality: The eventual storm (Cindy) was broad and disorganized, and eventually struck the Port Arthur area as a tropical storm; Run chosen: June 11, 00Z Hurricane Don :In reality: The eventual storm (Bret) was further south and weaker; Run chosen: June 8, 18Z Tropical Storm Emily :In reality: Nothing happened; Run chosen: June 22, 00Z Hurricane Franklin :In reality: ; Run chosen: July 1, 18Z; Author's note: The lowest explicit GFS pressure was 958 mb. To account for the coarseness of the GFS past 240 hours, a reduction function was utilized, bringing the pressure to 921 mb. KZC relationship applied to generate a 138 kt peak intensity for Emily. The highest reliably measured surface wind observation associated with Franklin was 102 mph at Cape Canaveral, with a gust of 119 mph. However, an unverified report from Coopers Town on Little Abaco Island indicated winds of 113 mph as Franklin passed to the north. A wide swath of the Florida coast and northern Bahamas experienced strong winds in similar fashion to Hurricane Matthew less than a year prior. Numerous trees were downed across the Space Coast in hurricane-force winds, with moderate damage reported at NASA's Kennedy Space Center; over 2.1 million people were impacted by power outages caused by Franklin. Damage in the state totaled US$3.4 billion. Due to the storm's path generally parallel to the southeastern US coast, the storm's strongest winds at landfall remained offshore. Despite being a major hurricane, no winds of such intensity were felt onshore. Sustained winds peaked at 97 mph on Hilton Head Island, damaging homes and downing power lines. At Savannah/Hilton Head Int'l Airport, winds reached 70 mph, with similar winds at Charleston, South Carolina. In both locations, wind damage was relatively minor aside from some scattered shingle and tree debris. Storm surge peaked at 12.9 ft (3.9 m) near Beaufort, South Carolina, and was responsible for much of the damage caused by Franklin. Large swaths of coastal regions were inundated in low-lying Beaufort County, South Carolina. Many areas were impassable and inundated for several days, if not weeks, in Beaufort County as well as adjacent coastal regions. Hurricane Gert :In reality: Nothing happened; Run chosen: July 10, 00Z; Author's note: The lowest explicit GFS pressure was 953 mb. To account for the coarseness of the GFS past 240 hours, a reduction function was utilized, bringing the pressure to 913 mb. KZC relationship applied to generate a 145 kt peak intensity for Gert. 80 kt/980 mb landfall on St. Vincent (July 15). 90 kt/967 mb landfall on San Pedro de Macoris in the Dominican Republic (July 17). 65 kt/986 mb landfall on Cat Island (July 19). 110 kt/947 mb landfall on West Palm Beach, Florida (July 20). 140 kt/915 mb landfall on the Mississippi River Delta and Grand Isle in Louisiana (July 22). :Honorable mentions: :: in Barbados + in Puerto Rico + in Nassau + in West Palm Beach (12z/July 6) in Panama City, FL (18z/July 6) in Homestead, FL + in Brunswick, GA (00z/July 8) in Wilmington, NC + in East Patchogue, NY (18z/July 9) off Cape Canaveral (12z/July 10) Tropical Storm Harvey :In reality: Tropical Storm Don behaved similarly; Run chosen: July 16, 12Z; Author's note: KZC generated 49 kt peak. ---- 12Z July 19: Upgrade to the GFS core Includes changes to Global Spectral Model components, Global Data Assimilation System, Tropical Storm Relocation, and Post-Processing ---- Hurricane Irma :In reality: ; Run chosen: July 24, 18Z; Author's note: KZC generated 96 kt peak at 384 hours. Intensification past that point based on previous trends and some creative license. Hurricane Jose :In reality: ; Run chosen: August 4, 00Z Extratropical remnants persisted until August 21. :Honorable mentions: :: in South Carolina (00z/August 3) Hurricane Katia :In reality: Hurricane Franklin', 75 kt peak; Run chosen: August 6, 06Z Landfall at peak intensity at 08:15 UTC near Tamiahua. Tied for strongest storm in the Bay of Campeche by pressure with Hurricane Karl (2010). Hurricane Lee :In reality: Hurricane Gert, 95 kt peak; Run chosen: August 14, 12Z for most of the track, with August 14, 00Z used for some earlier parts of the track. Hurricane Maria :In reality: Invest 92L. Remained weak; Run chosen: August 13, 06Z Season effects Fun Images Category:Reimagined seasons Category:Atlantic hurricane seasons Category:2017 Atlantic hurricane season